On Friday, 2 February 2024 21:47:00 GMT Dominique Martinet wrote: > So I think Florian is correct in that barriers won't be issued on > these disks, and if they internally have such a cache it'd probably be > unsafe... > > Now does the disk itself know that it's in such an enclosure and > properly behaves as write through? > I think we'd have a lot more corruptions on our hands if it was > incorrect here, btrfs in particular is very sensitive to disks that > lie with barriers but I'm not sure how much it's used on such drivers. > As far as I can tell, having owned such an enclosure in the past, it doesn't tell the drive anything - it relies on the fact that SATA drives write back fairly aggressively when the command interface is idle, and thus the cache is fully written back to the medium when it's idle for a few seconds. If you go through the sequence "remove safely", then wait for UI confirmation, then unplug the USB port, it'll usually have written back the cache before you physically move your hands to the USB cable. As these enclosures aren't particularly fast (for example, commands must complete in issue order, rather than being able to complete out of order as in TCQ/NCQ), I suspect most users of them don't use btrfs or xfs on them (I'd expect ext4 if Linux-only, FAT32, exFAT or NTFS if shared between OSes); they're basically intended to let you have a huge "thumb drive" for machine- to-machine transfer, and they're fine in that use case. On the other hand, turning on the "sync" mount option doesn't help with these enclosures; if anything, it'll make things worse by increasing the number of commands in flight which have to be handled before the drive switches to cleaning its cache. -- Simon Farnsworth -- _______________________________________________ devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@xxxxxxxxxxxxxxxxxxxxxxx Do not reply to spam, report it: https://pagure.io/fedora-infrastructure/new_issue
